1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to a configuration of a discharging roller pair that delivers a sheet in that image forming apparatus.
2. Description of the Related Art
Heretofore, as an image forming apparatus such as a copier, a laser printer, a LED printer, a facsimile machine, a word processor and multifunction devices of these, there is an image forming apparatus that forms an image on sheets by using an electrophotographic image forming method. In such an image forming apparatus, in general, sheets are supplied one by one to an image forming unit from a sheet feed tray in which a large number of the sheets are stacked and housed, an image is formed on the sheets in the image forming unit based on an image signal inputted thereto, and thereafter, the sheets are delivered to an outside of the apparatus. As such an image forming apparatus, there is one capable of duplex image formation (duplex printing) in which the image is formed on one surface (first surface) of each of the sheets, thereafter, the sheet is reversed by a reversing unit and is conveyed to the image forming unit again, and the image is formed on an opposite surface (second surface) of the sheet.
As a method for the reversing unit of the image forming apparatus capable of the duplex image formation, there is a method of performing a switchback operation for the sheet and reversing the sheet in such a manner that delivery rollers which deliver the sheet to the outside of the apparatus are made capable of positive and reverse rotations, and the delivery rollers are rotated positively and reversely. In the reversing unit of such a switchback method, in the case of reversing the sheet, first, the sheet is delivered partway onto a delivery tray by the delivery rollers in a state where a trailing edge of the sheet in a conveying direction is held. Next, a rotation direction of the delivery rollers is switched to a direction reverse to a delivery direction, whereby the trailing edge of the sheet in the conveying direction is turned to a leading edge thereof, and the sheet is fed into a duplex conveying path for such second surface printing.
With regard to such an image forming apparatus that performs the switchback operation for the sheet and feeds the sheet into the duplex conveying path, in order to correct skew feed of the sheet, which occurs at the time of the switchback operation, a technology for providing a skew feed correction mechanism in a unit of conveying the sheet immediately after being subjected to the switchback operation is disclosed. As such a preliminary skew feed correction method by the skew feed correction mechanism, it is general to use a hit correction method of hitting the leading edge of the sheet under conveyance against a predetermined skew-correcting portion and correcting the skew feed of the sheet (refer to Japanese Patent Application Laid-Open No. 2003-155146).
In the case where the conveying force of the delivery rollers is excessively large when the leading edge of the sheet hits against the skew-correcting portion in the skew feed correction mechanism, there occurs a case where the leading edge of the sheet passes through the skew-correcting portion in a state of not being aligned sufficiently, and a sufficient skew feed correction effect is not obtained.